Cellular networks known as Public Land Mobile Networks (PLMNs) provide voice and data connectivity to mobile devices across a large geographical area, typically a country. Each cellular network is operated by a mobile network operator (MNO) and is formed of a mobile network core, in LTE networks known as an Enhanced Packet Core (EPC), with a number of macrocell radio stations, known in LTE as Enhanced NodeBs (eNodeBs), located at the edges of the network.
In the UK there are several mobile network operators (MNOs), each owning and operating a separate band of licensed spectrum to carry the network signals. In addition to MNOs, there are Mobile Virtual Network Operators (MVNOs) which use one or more of the MNO physical networks to offer mobile service to users at a different cost.
In each case of MNO and MVNO, the identity of the mobile network is broadcast by the macrocells in the form of a Mobile Country Code (MCC) and Mobile Network Code (MNC) pair which provides a globally unique identity for each mobile network.
Each handset can only connect to a single PLMN at a time. Each subscriber of a cellular network has a Universal Integrated Circuit Card (UICCs), commonly, but incorrectly, referred to as Subscriber Identity Module (SIM) cards which have been issued by the MNO or MVNO containing, among other things, the authentication credentials for accessing the respective network. Furthermore, each UICC includes a central processor and application code to run a Universal Subscriber Identity Module (USIM) application for controlling access to Universal Mobile Telephone System (UMTS) and Long Term Evolution (LTE) cellular networks.
When a mobile device is switched on and the mobile device scans for surrounding base stations and presents the list of detected base stations to the USIM. The USIM determines which base stations are owned by the appropriate MNO, MVNO, and provides information to the handset to allow it to authenticate and connect to the macrocell of the appropriate MNO network.
As part of the connection process, the USIM is responsible for determining a network name to be displayed to the subscriber so that they know which network they are connected to. This is especially important in the case of international roaming where the MNO has no local presence and relies on a commercial agreement with a foreign network to provide connectivity at increased cost.
When connected to the PLMN, the handset will display the same MNO network name when it is connected to any of the MNO's macrocells. The macrocells all have the same configuration and therefore are capable of offering the same services.
Whilst macrocells provide wide area geographical network coverage, they are large devices and therefore are costly to install. Furthermore they require a high capacity backhaul network link to the EPC. Recently, short range cellular base station devices known as small cells (the term covers femtocells and picocells) are being deployed by MNOs in order to extend and supplement the coverage of the macrocells and to provide additional network capacity in densely populated areas. The small cells provide cellular coverage over a range of up to 200 m and use a consumer broadband connection to backhaul data to the MNO core.
Small cells are beneficial to the MNOs are they can easily provide additional coverage in certain geographical areas while also reducing strain on the existing macrocells because the traffic is backhauled without requiring further investment by the MNO.
Generally, the quality of experience for a subscriber is also improved because they have a more reliable cellular signal, especially in densely populated areas or areas where the macrocell signal is poor. The handover and idle mode reselection mechanisms from the macrocells and small cells, small cells to macrocells and small cells to small cells is also no different to typical macrocell to macrocell migration. Therefore the presence of small cells in the network is transparent to a subscriber. The entire radio access network (RAN) of the PLMN is presented as a single network.
A problem with the transparent setup in the RAN is that although macrocell eNodeBs and small cells have very different hardware and service capabilities, they are presented as being homogenous access points into the PLMN and therefore the mobile device and subscriber are not made aware of any services that a particular type of base station device is able to provide.